1. Field of the Invention
The present invention relates to a method of manufacturing a glass molding obtained by press molding a molten glass drop.
2. Description of the Related Art
In recent years, a glass optical element is widely used as a lens for digital camera, an optical pickup lens for DVD or the like, a camera lens for cellular phone, a coupling lens for optical communications, and the like. A glass molding manufactured by press molding a glass material with a mold is widely used as such a glass optical element.
As a method of manufacturing such a glass molding, a method of producing beforehand a glass preform having a predetermined mass and shape, and heating and press molding this glass preform with a mold to obtain a glass molding (hereinafter also referred to as a “reheat press method”), and a method in which a dropped molten glass drop is received by a lower mold, and the received molten glass drop is press molded to obtain a glass molding (hereinafter also referred to as a “droplet molding method”) are known.
Attention is being focused on the droplet molding method since a glass molding can be manufactured directly from a molten glass drop without the need to repeat heating and cooling of a mold and the like, which can significantly shorten the time required for a single molding. A method of manufacturing a glass molding using such a droplet molding method is disclosed in Japanese Laid-Open Patent Publication No. 61-146721.
In the method of manufacturing a glass molding using the droplet molding method, the position of a molten glass drop with respect to a molding surface of a lower mold when the molten glass drop is dropped onto the lower mold is of importance for improving the glass molding in precision.
U.S. Pat. No. 7,415,842 defines the shape of a lower mold and the drop amount of a molten glass drop such that space is left between the molding surface of the lower mold and the molten glass drop at the border between the molding surface of the lower mold and the outer peripheral surface.
In recent years, further improvement in precision is demanded of glass moldings while miniaturization of glass moldings is required, which raises an issue of reduced manufacturing yield.